Method of molding dentures



March 12, 1940. R, w, ERDLE 2,192,902

METHOD OF HOLDING DENTURES Filed Jan. 2o, 193s 2 sheets-sheet 2 PatentedMar. 12, 1940 UNITED STATES METHOD OF MOLDING DENTURES Reiner W. Erdle,Chicago, Ill., assignor to Dental Research Corporation, a corporation ofIllinois Application January 20, 1936, Serial No. 59,816

2 Claims.

rlhis invention relates to dentures and has to do with an improvedmethod of producing porcelain and metal combinations for dentures anddental parts, and with an improved porcelain and metal combination fordevices of this sort.

It is to be understood that the invention is lnot limited to theparticular devices with which I shall describe the same hereinafter inconnection with the drawings.

Porcelain and metal combinations have been produced before but they haveinvolved great labor cost, and the results have not always been as goodas desired. Heretofore, the porcelain part has been produced by abuilding up process involving a number of firings or bakings, i. e., aring or baking process after each installment of porcelain. There areonly a few mechanics in this country who are skilled enough to build upvdevices of this type, and this is the reason why devices produced inthis manner have not been profitable.

One of the main objects of the present invention is to produce porcelainand metal combinations for dentures and dental parts without thebuilding up and repeated firing or baking processes of theprior art andin a simple and inexpensive inanner which will produce uniformly goodresults without requiring any exceptional skill on the part of themechanic.

30 Another object is to provide an improved porcelain and metalcombination for dentures and dental parts wherein the metal part of thedenture or appliance embodies a high degree of rigidity as measured bymodulus of elasticity.

Further objects and advantages and numerous adaptations of the inventionwill be apparent from the following detailed description taken inconnection with the accompanying drawings in which:

40 Figure l is a perspective View of one form of completed porcelain andmetal denture embodying the present invention;

Figure 2 is a more or less diagrammatic sectional view showing themethod of and means for 45 forming the denture shown in Figure l, inaccordance with the present invention;

Figure 3 is a bottom plan view of the metal base of the denture shown inFigures 1 and 2 before application of the porcelain thereto;

Figure 4 is a sectional view taken on the line 4--4 of Figure 1;

Figure 5 is a side elevational view, partially in section, showinganother form of appliance formed in accordance with and embodying the,5,5l present invention; and

Figure 6 is a perspective view showing another form of applianceconstructed in accordance with and embodying the present invention.

Referring to the drawings, the denture shown in Figures 1 to 4,inclusive, is in the form of a dental plate which may be either full orpartial. This plate comprises a metal base 5 and a porcelain gum part 6having porcelain teeth l,"which may be either stock teeth to which thegum part 6 is molded or teeth molded in one piece With the lo gum part.

The base 5 is preferably formed of a metal embodying a high degree ofrigidity as measured by modulus of elasticity so as to prevenu unduedeflection under imposed loads and to supu port and strengthen theporcelain partl of the denture. A metal with a rigidity comparable withor exceeding that of the porcelain is preferably employed. A metal likethat disclosed in Charles H. Prange Patent No. 1,958,446, dated 20 May15, 1934, or like that disclosed in the copending application of CharlesH. Prange, Serial No. 725,651, led May 14, 1934, is suitable for use inconnection with the present invention. I do not, however, intend to belimited to these par- 25 ticular metals as other metals having thedesired rigidity may be employed, and so far as the broader aspects offorming the porcelain and metal combination are concerned, metals suchas high fusing white gold without this characteristic of rigidity asmeasured by modulus of elasticity may be employed.

The metal base 5 is formed at 8 to nt the alveolar ridge, and thesurface 9 to which the porcelain gum part 6 is molded is preferablyprovided with retention means. The particular retention means showncomprises a plurality of wires l0 crimped throughout their length andspot-welded or otherwise secured at spaced locations at H to the surface9.

Unless the porcelain and metal have the same coeflicient of expansion,it is desirable to provide a layer l2 of ceramic material or metalbetween the denture metal and the porcelain in order to prevent checkingof the porcelain. This layer |2is preferably of a somewhat yieldingmaterial to relieve the porcelain of stresses resulting from differentthermal expansion and contraction between the metal and the porcelain.

The layer I2 may be applied over all surfaces 50 9 of the metal part ofthe denture, to or around which the porcelain is to be molded, andaround the retention means Il). 'Ihis coating may be sprayed upon thedenture metal or otherwise applied as a, coating thereto as by paintingthe same on the denture metal, and where the coating is a ceramiccoating, it comprises a refractory material and a binder, such as silicaand silicate of soda, silica and tetra-ethyl silicate, or a mixture ofsilica (refractory), finely ground asbestos (plasticizer), naphthalene(for creating porosity), and a binder of organic silicate or sodiumsilicate or the like. Of course other refractories like alumina,zirconia, or the like, may be used. Plasticclay is another satisfactorybinder, and it may be used as a binder for the refractory aggregate inthe same manner as the other binder above mentioned.

One satisfactory material for the coating l2 may be formed by mixingpowdered int with a mixture of 50% of silicate of soda, diluted ten toone, and 50% of a mixture of diluted di-glycol stearate. To 100 c. c. ofthis paste is added one c. c. of hydrochloric acid to effect the settingof the paste. This paste is sprayed to or otherwise applied as a coatingon the denture instal, as above set forth. Potassium carbonate may alsobe used with this material up to 10% with desirable results.

Another material for forming the coating i2 between the porcelain andthe denture metal may be formed by mixing about ten to twenty partswater to one part silicate of soda and powdered fiint to make a pastethat may be sprayed upon the denture metal or otherwise applied as acoating as by painting the same on the denture metal.

instead of making this coating of the material above described, it maycomprise a hydrolyzed binder composed of tetra-ethyl silicateapproximately 50 alcohol approximately ll0%, and water approximately10%. The actual procedure of hydrolyzing the tetra-ethyl silicate isgenerally as follows: First take the fifty parts by volume oftetra-ethyl silicatey add the forty parts of alcohol, and shakethoroughly. Then add the ten parts by volume of water slightlyacidulated with approximately .007% of hydrochloric acid. Powdered dintand asbestos are also added to make a paste that may be applied to thedenture metal as above set forth. l The definite percentages may, ofcourse, vary widely within the scope of the present invention.

In making up this coating, clay, or any other highly refractory materialmay be used with or in lieu of the flint content of the coating.

Instead of forming the layer l2 of ceramic material, this layer may beformed of metal foil, such as platinum or gold foil, adapted to thesurface 9 of the metal base 5 of the denture and spot-welded to retainit in place.

A wax or other meltable pattern is then adapted to or formed upon thesurface S of the metal plate 5 to the desired shape and configuration ofthe porcelain gum part of the denture. The teeth 'l are set up andarticulated on the wax pattern. As already explained, these teeth may bestock teeth formed of porcelain, or wax teeth may be used to form theporcelain teeth as a unitary part of the porcelain gum part 6.

The wax pattern is attached to a sprue which is large enough to hold theamount of porcelain required to fill the mold. The sprue, metal base 5,and wax pattern and teeth 'l are then -coated at lli with a materialwhich will not combine with the fused porcelain and which, at the sametime, will give the mold cavity a smooth finish. This material may besimilar to the material forming the ceramic layer i2 between theporcelain and metal parts of the denture, as above mately 40%,

described. The material formed by mixing powdered flint with a mixtureof 50% of silicate of soda, diluted ten to one, and 50% ofI a mixture ofdiluted di-glycol stearate with one c. c. of hydrochloric acid added to100 c. c. of this paste to eifect the setting of the paste is suitablefor this purpose. As before, this paste is sprayed to or otherwiseapplied as a coating over the entire assembly, and potassium carbonatemay be added up to 10% with desirable results. Or this material may beformed by mixing about ten to twenty parts water to one part silicate ofsoda and powdered flint to make a paste that may be sprayed upon themetal, wax pattern, and teeth, or painted thereon. Or it may be made ofa hydrolyzed mixture of tetra-ethyl silicate approximately 50%, alcoholapproxiand water approximately 10%. This solution is acidulated withapproximately .007% hydrochloric acid, and powdered flint and asbestosare added to make a paste that may be applied as above set forth, or anyother highly refractory material which will not combine with the fusedporcelain and which is finer than the rough outer investment material,may be used with or in lieu of the flint content of the coating id.

When this coating is applied, the water evaporates and leaves a coatingwhich will not combine with the fused porcelain, and which, at the sametime, gives the mold cavity a smooth finish which cannot be obtainedWith the rough outer investment material. It is thought that thiscoating absorbs the tetra-ethyl binder of the investment material wherethat material is like the investment material disclosed in my copendingapplication Serial No. 48,071, filed November 4, 1935.

rlhis coating. i4 also prevents oxidation of the metal part 5 of thedenture during the molding of the porcelain part thereon, as willhereinafter be described.

The coated metal base with the wax pattern on the surface 9 thereof, andthe teeth 'I set in the wax pattern, is then placed in an investmentflask or ring i0 and embedded in the investment material forming thebody I1 of the mold. The ring I6 is preferably formed of- Nichrome, orany metal alloy which retains its strength at high temperatures. Toprotect the ring I6 against oxidation and so that the metal will notburn oi when the ring is subjected to high temperatures for relativelylong time intervals, this ring is preferably coated with a clay wash orother wash suitable for this purpose. This wash may be applied byspraying the same on the ring or dipping the ring therein, or otherwiseas desired.

instead of making the ring It of a metal alloy, this ring may be made offire-clay or any ceramic material which retains its strength at hightemperatures.

The body Il of the mold is preferably formed of van investment materialwhich has thermal characteristics which are compatible with the thermalcharacteristics of the porcelain which is being molded. Breakage andinaccuracy of the product are avoided, and the results are highlysatisfactory,

The refractory mold material which I employ has a thermal expansion uponheating, as distinguished from a permanent expansion or contraction, sothat when it comes back to room temperature it will have the originaldimensions. That is, there preferably is no appreciable permarientexpansion or contraction as a result of heating, but the mold materialexpands as a result of thermal expansion while it is heated, andthereupon contracts again upon cooling to room temperature. This isimportant because the porcelain which is being molded is necessarily atthe same high temperature as the mold while it is being molded, and itmust necessarily shrink when it is brought down to room temperature.

The thermal expansion of the mold may be controlled, depending upon thecomposition of the mold material. Fused quartz may vbe added to themixture to reduce the thermal expansion, or cristobalite may be added toincrease the expansion. Also, other materials, such as alumina, may beused in admixture for similar purposes.

Fused quartz, ground to pass through a sixtymesh sieve, with some largerand finer particles, and an addition of approximately one-fifth byvolume of finely ground pure iiint makes an excellent refractory bodyhaving the properties and advantages above set forth. This material has'thermal characteristics compatible with the thermal characteristics ofthe porcelain upon heating to the relatively high temperatures where theporcelain starts to flow. These temperatures are approximately 1700 F.to 2000" F. for low fusing porcelain, approximately 2000 F. to 2300 F.for medium fusing porcelain, and approximately 2300 F. to 2500o F. forhigh fusing porcelain.

Ground iirebrick of coarser mesh, i. e. about to 40 mesh, may beemployed in lieu of the fused quartz referred to in the precedingparagraph. v

This highly refractory investment material is used in amount to form thebody i7 of the mold, and I admix therewith in amount to serve as abinder for the refractory investment material, as disclosed in mycopending application Serial No. 27,566, filed June 20, 1935, a bindersuch as that more fully disclosed in Unitedl States Letters Patent No.1,909,008, dated May 16, 1933, to Charles H. Prange.

As disclosed in the foregoing patent, this binder is preferably composedentirely of pure silica gel. As pointed out there, silica gel, asis wellknown, is a colorless and transparent substance which exists in varyingdegrees of firmness. When it embodies a large amount of water it is softand pasty, like gelatine, and when it is dehydrated it becomes extremelyhard, glassy and brittle.

Silica gel is` available on the market in its hard and glassy condition,but so far as is now known there is no practical Way of utilizing it inthis condition to serve the purpose of the prior patent, or for thepurpose of the present application. This form of the mold body i7 of thepresent invention therefore involves the procedure of the prior patent,whereby pure silica gel may be caused to be generated, in situ, in aplastic mixture, as will hereinafter appear.

As in the above patent, 1 resort to the characteristic of colloidalsilicio acid to Yundergo a spontaneous sort of transformation, wherebysilica gel is generated or formed in a continously increasing manner.The exact chemical transformation which silicio acid undergoes is notfully understood, but there is apparently a spontaneous and increasingaggregation of colloidal silica particles resulting, ultimately, in acomplete conversion of the silicio acid into what is commonly known assilica sel.

The binder which I employ in accordance with this form of the mold bodyof the present invention is a substance which is adapted in theforegoing `general manner to form or generate pure silica gel. `Morespecifically, it has been found that certain organic silicates,preferably silicon esters, when hydrolyzed and slightly acidied, areadmirably characterized by the ability to undergo a spontaneoustransformation with the ultimate generation of nothing more than puresilica gel.

For example, in the preferred method of forming the investment materialfor the mold body Il, a silicon ester of the general class whichincludes, e. g., tetra-ethyl silicate, tetra-butyl silicate,tetra-methyl silicate, glyceryl silicate, or diglycol silicate, isconditioned or treated by the addition of a slight amount of anacidifying agent, and, by the addition of water, if necessary, toproduce a liquid or semi-liquid susbtance which is satisfactorily usableas a binder to form a paste or plastic mixture with the refractoryfiller above described. Such mixture is adapted to be poured, handled,or manipulated in a suitable manner and is characterized by an abilityto set or harden without a drying out process. This action is probablydue to a formation of a colloidal silicio acid and to a subsequentspontaneously increasing transformation of the silicio acid into asilica gel, the latter ultimately becoming more and more dehydrateduntil it is entirely solid.

The setting of the material may be accelerated in a variety of ways, as,for example, by heat; but, in practicing the present invention, I preferto incorporate with the plastic mixture a slight amount of suitableaccelerating agent whereby the setting is sufciently complete to permithandling within a short time. Magnesium oxide powder may be used for theaccelerating purpose, although other accelerating agentsare contemplatedwithin the scope of the present invention. I-Iexamethylenetetramine(C6H12N4) is a very satisfactory accelerator and has the advantage that,in being organic, it will be completely eliminated in the firingoperation.

I find that insead of using an accelerator, the desired acceleratedsetting may be obtained by increasing the acidity of the binder.

The general nature o-f the preferred investment material of the presentinvention and the essential features thereof, as well as the numerousadvantages achieved thereby, will be more fully understood by morespecifically setting forth an illustrative example. It is to beunderstood, however, that the procedural steps and the proportions ofthe parts and other details, as hereinafter set forth, are given merelyby way of illustration and are capable of wide variations to suitdifferent requirements.

One method of making the mold or investment material which has proven tobe satisfactory consists in first producing a binder by properlytreating and conditioning liquid tetra-ethyl silicate. With about eightvolumes of this organic silicate, I mix about one volume of water and atrace of a suitable acidifying agent, e. g., a few drops of hydrochloricor sulphuric acid, thereby inducing a partial hydrolysis. Since theseliquids will not readily mix, it is preferable to add a small amount ofa material which is miscible with all. For example, I prefer to add oneor two volumes of ethyl alcohol or acetone whereby a true and thoroughmixture of the liquid is readily produced. This common solvent may beomitted, and a high speed mechanical agitation employed to obtain thedesired miscibllity. The amount of acid to be used Will vary withrequirements, but shouldbe, preferably, just sufficient to make themixture very slightly acid when tested With litmus paper.

The mixture may then be stirred on a Water bath until a sample, upondrying upon the hand, for example, is sticky to the touch or otherwisetested and found to be in suitable condition. Usually a period of one totwo hours will suffice.

This produces the binder heretofore referred to and having thecharacteristics hereinbefore mentioned. And this binder may be usedimmediately, or it may be stocked for a reasonable period of time, to beused when required.

In making up the investment material I mix approximately four parts ofthe investment material, as above described, with about one part of theliquid binder. There will be some variation in the amount of binderused, depending upon the type of material and upon the type ofinvestment material, the foregoing proportions being suitable for makingup an investment material in accordance with this invention and for thepurposes herein set forth. The excess binder may be readily eliminatedby vibrating the composition to cause the solid parts thereof to settle,and to cause the excess liquid to rise to the tcp. The liquid binderwhich comes to the top in the vibrating process may be poured olf. It isto be understood that to start with the proportions of one part liquidbinder to four parts of refractory filler are approximately correct, butthat in the manipulative procedure the mass of filler with the liquidbinder is subjected to vibration over a period of time which settles theller in a compact mass at the bottom and changes the liquid solid ratiofrom the proportions when first mixed. If preferred, a relativelygreater proportion of filler may be used, in which case the plasticcomposition of refractory filler and binder may be produced by kneadingit.

This plastic material will normally set in a period of three to sixdays, but the speed of initial setting is preferably increased by eitherof tWo methods.

One satisfactory porcedure lies in heating the mixture in an oven toapproximately 11G-115 C. This heating apparently speeds thetransformation of the colloidal silicio acid into colloidal silicaparticles, and an initial set can be secured in approximately an hour orless.

The method which I prefer to use to speed the initial setting of themixture is to incorporate with the pasty material a trace of suitableaccelerating agent. While various materials Will do, I have found anaccelerator of the class hereinbefore set out to be extremelysatisfactory and preferable for this purpose. A trace or slight amountof this accelerating agent is suicient, and I prefer to use it by mixingit directly with the refractory ller before the pasty material isproduced. In carrying out this procedure, I use about one part by Weightof the accelerator to one thousand parts by weight of the refractoryinvestment material. This is equivalent to one-tenth of one per cent byweight. The composition, when thus produced, takes an initial set inabout half an hour or less.

While I cannot fully explain the action of this accelerating agent, Ihave found that a variety of accelerators may be used. Theseaccelerators may be of a character to be completely or practicallyeliminated by heat, thereby leaving the mold free, or substantiallyfree, of extraneous inorganic solids. Where the accelerating agent is aliquid, it is preferably mixed with the binder and where it is a solid,it is preferably mixed with the refractory ller.

After making the investment material as above set forth, this materialis poured or otherwiseintroduced in plastic form into the aslr or ringIt in which the coated denture assembly, comprising the metal part, Waxpattern and teeth 1, has been placed and the metal part, Wax pattern andteeth, and sprue or gate forming part are completely embedded in thisinvestment material. After the ring It has been filled with investmentmaterial with the sprue or gate forming part projecting therefrom, themold body il is set and the Wax pattern is eliminated, leaving the fixedmolding cavity 2U lined with the coating material i4 for obtaining theVdesired smooth finish and which, at the same time, Will not combine withthe fused porcelain, and which protects the metal part 5 againstoxidation and the sprue or gate opening 2i opening vertically from thetop of the mold. The sprue or gate opening E! is preferably of adiameter of about one-half to three-quarters of an inch, and ispreferably restricted at 22 to facilitate removal of the procelainprojection formed at the lower end of the sprue or gate opening inmolding the porcelain part of the denture.

I find also that mixtures of refractory material with plaster of Parisas a binder may be successfully used, and I contemplate such materialsas a mold material suitable for use in connection with the presentinvention in lieu of the mold material previously described.

These plaster investments may be made up, for example, of one part ofhydrocol, one part of finely ground or powdered int, ve parts of groundfirebrick, and a small amount of boric acid, borax, feldspar, epsomsalts, or any material which will flux the investment body at elevatedtemperatures to give the desired strength.

An investment in which plaster is the binder and fused alumina, fusedmagnesio., ground quartz, pulverized alumina, or other known refractorymaterials may be combined to form a suitable investment.

After the foregoing operations, the porcelain, in powder or rock form,is inserted in the opening 2i left by the sprue. If more than one shadeof porcelain in the denture or denture part is required, the combinationof the desired color porcelain rmay be inserted in the sprue in theorder and amount to produce the desired effect of shade variety ofdenture or denture part. The mold is then placed in a suitable furnace,indicated more or less diagrammatically at 25. The interior of thefurnace 25 is provided with a base 2% for supporting the mold body inits flask or ring l in raised position. Where the teeth 'l are stockteeth, the mold body ill supports these teeth in proper position withrespect to each other during the time the porcelain is being placed inthe mold and While the porcelain is heated and pressed into the cavityto fill the same and until it has cooled and set with the teeth firmlyanchored therein. The mold body li also supports the metal part 5 inproper position with respect to the mold cavity and with respect to theteeth, where the teeth are stock teeth formed of porcelain.

The furnace 25 is then heated with as little heat as required to enablethe porcelain to flow into and fill the mold cavity Z8 formed by theelimination of the Wax pattern and, Where the teeth are formed of Wax,by the elimination of these wax teeth to ll such cavity throughout. Thedesired pressure for pressing the porcelain into the mold cavity 2|] maybe imposed by weights 2l at the lower ends of arms 28 on the frame 29which may be disposed externally of the furnace, as shown. In onepractical embodiment of the invention, a weight 2T of about fourteen.pounds at the lower end of each of the arms 28 was found to besatisfactory. The lower end of the center arm 30 rests upon a plunger orbutton 3l which lits relatively snugly in the sprue or gate opening 2|,and presses the porcelain, indicated at 32, ahead ofA it and into themold cavity under the influence of the weights 27|. The arm 30 operatesslidingly through an opening in the upper wall of the furnace 25. Thisarm 30 and the button 3| may be formed 0f non-metallic material, such aslire-clay or other ceramic material.

In ay practical embodiment of the invention, the heat was raised untilthe plunger 3| started to move downwardly and the molding process wascarried out with a temperature from ape proximately 100 degree F. to 200degrees F. below the normal fusing point of the porcelain. This is animportant aspect of the present invention. A porcelain consisting ofabout 30% china clay, 25% Feldspar and 45% calcined alumina has a fusingpoint of approximately 3200 degrees F. but becomes plastic and moldab-leat about 2800 degrees F. This indicates that very high fusing porcelainsmay be molded at temperatures considerably below the normal fu'singpoint. Cverheating with the objectionable results thereof are avoided,and a strong, dense porcelain without discoloration is assured. Heatingbelow the normal fusing point of the porcelain not only produces astrong, dense porcelain without discoloration but a porcelain in whichthe translucency is increased; also Very high fusing porcelains can behandled without exceeding the refractory limits of the mold materialsavailable. At the same time, by pressing the porcelain into the moldcavity 20 while heated suniciently to ow into and iill said'cavity andWithout discontinuing the heat while the porcelain is being pressed intothe cavity, chilling of the porcelain is avoided, and exceedingly thincavities of large extent may be lled throughout. The resulting porcelainpart isof uniform and exceedingly ne physical characteristics, and thebuilding up and repeated firing or baking processes of the prior art areavoided.

After the mold cavity is completely filled, the molded article isallowed to cool slowly, and when cooled, is removed from the mold. Theinvestment material forming the mold body l'l sinters but does not fuseduring `the ring process. Therefore it can be removed from the dentureor other article with a steel brush, or by picking it away from thearticle.

Instead of placing all of the porcelain in the gate and filling the moldby pressing the porcelain from the gate into the mold cavity, it ispossible to do it somewhat diiferently, namely, to grind up theporcelain to fairly fine fragments, make a paste of it with water oralcohol, and then to vibrate it down into the mold cavity so assubstantially to lill it. Additional porcelain is placed in the gate.The whole assembly is placed in the furnace and the procedure from thenon is as above described. The difference is that only the amount ofporcelain necessary to complete the lling of the mold cavity is fed infrom the gate by the process previously described.

The porcelain gum part 6 is molded against and thereby joined to themetal part and, as a result, these two elements are not required toV bejoined afterthe porcelain is removed from the mold.

After the denture, indicated as a full denture in Figurel, is removed,the porcelain gum part E and, if desired, the teeth may be stained andglazed to suit the requirements.

If porcelain having substantially the same co- Aprepared portions 42 ofthe natural teeth, the

roots of which are illustrated at 42. The gum line is shown at 42".

The bar l0 and copings 4| are preferably formed of a metal embodying ahigh degree of rigidity as measured by modulus of elasticity, `as setforth in connection with the metal part of the preceding embodiment ofthe invention.

Unless the porcelain and metal have the same coefficient of expansion,it is desirable, as before, to. provide a layer 413 of metal or ceramicmaterial between the denture metal and the porcelain in order to preventchecking of the porcelain. This layer L13 may be formed of platinum orgold foil adapted to the surfaces of the bar and copings 4|, andspot-Welded to retain it in place. Instead of forming this layer ofmetal, it maybe formed of ceramic material as set forth in connectionwith the preceding embodiment of the invention.

A Wax or other meltable pattern is then adapted to or formed upon thebar 4l] and copings 4| to the desired shape and configuration of theporco-- lain teeth 45. 'I'he Wax pattern is attached to a sprue, and theentire assembly is coated and invested as described in connection withthe preceding embodiment of the invention, whereupon the wax iseliminated. The porcelain is then introduced into the opening left bythe sprue and may be shaded as previously explained, and the mold isplaced in a suitable furnace which is heated, and, simultaneously withthe application of this heat, the porcelain is pressed slowly andcontinuously into the mold cavity and molded to the bar 4i) and copings4| in the manner set forth in vconnection with the preceding embodimentof the invention.

The denture shown in Figure 6 is` a typical lingual bar type denture. Itcomprises a lingual bar 5i) which is preferably formed of a metal havinga high degree of rigidity as measured by modulus of elasticity, as setforth in connection with the metal parts of the preceding embodiments ofthe invention.

As before, unless the porcelain and metal have the same coefncient ofexpansion, a coating 5| of somewhat elastic character is applied to theportion 5i of the bar 50 or around which the porcelain 52 is molded.This coating 5| may be a coating of ceramic material or a metal foil, asdescribed in connection with the preceding embodiments of theinvention.` A wax or other meltable pattern is then adapted to or formedupon the coated portion 5i' of the bar 5@ to the desired shape andconfiguration of the porcelain part 52, and the teeth 53 are set up andarticulated on the wax pattern. These teeth may be stock teeth formed ofporcelain, or wax teeth may be used to form the porcelain teeth 53 as aunitary part of the porcelain part 52.

The wax pattern is attached to a sprue and the entire assembly iscoated, as beore, and invested, whereupon the wax is eliminated and theporcelain introduced. The mold is then introduced into a furnace whichis heated to enable the porcelain to flow into and ll the mold cavityand, simultaneously with the application of such heat, the procelain ispressed slowly and continuously into the mold cavity and molded to oraround the coated portion 5I of the bar Eil, as more fully set forth inconnection with the preceding embodiments of the invention.

Clasps 55 are secured to the bar 5t for anchoring the denture to thenatural teeth, as well understood in the art. These clasps may be formedof Vitallium or any other suitable` clasp metal fastened to the bar 5@by spot-welding, or they may be formed as a unitary part of the har 50,or otherwise suitably attached thereto.

The portion 58, or any other desired portion oi the lingual bar 50, maybe provided with a porcelain gum part having a tooth or teeth thereonsimilar to the parts 52 and 53 shown and described.

I do not intend to be limited to the precise g details shown ordescribed.

I claims' 1. The method'oi forming a denture having a metal part and aporcelain part, which comprises forming a mold cavity contiguous to themetal part, heating said cavity prior to filling same with porcelain,heating the porcelain outside said cavity to a temperature at which itwill iiow into said cavity, simultaneously with the heating of thecavity and the porcelain subjecting the heated porcelain to pressure toforce same into the cavity to iill all portions of the cavity and moldthe porcelain part to shape contiguous to said metal part, andsimultaneously with the molding of said porcelain part to shape joiningsame under heat and pressure to said metal part.

2. The method of forming a denture having a metal part and a porcelainpart, which comprises applying a coating to the metal part, forming amold cavity contiguous to the coated .surface of the metal part, heatingsaid cavity prior to iilling same with porcelain, heating the porcelainoutside said cavity to a temperature at which it will flow into saidcavity, Vsimultaneously with the heating of the cavity and the porcelainsubjecting the heated porcelain to pressure to force same into thecavity to fill all portions of the cavity and mold the porcelain part toshape contiguous to the coated surface of said metal part, andsimultaneously with the molding of said porcelain part to shape joiningsame under heat and. pressure to the coated surface of said metal part.

REINER W. ERDLE.

